Windscreen wipers are provided with a vertebra and a blade rubber. The blade rubber has one or more slots or recesses to receive one or more rails. The rails may be in the form of a flattened wire or a wire with a rectangular cross-section. According to the prior art, these rails form the vertebra.
EP 1819559 by applicant also describes vertebrae having rails of different shape and rubber blades having different angled recesses for fitting in said rails.
In what is often referred to as a “flat blade”, the rail is a flattened or rectangular wire or has been made of sheet metal. The rail functions as a spring which transmits forces to the blade rubber to hold the blade rubber in good contact with the surface of the windscreen. Therefore the rail is bent stronger than the glass face and acts as e.g. a leaf-spring member. There can be one or more rails in a flat blade wiper. When a pressing force from a wiper arm is applied to the blade rubber, the leaf-spring member is elastically deformed until it conforms with and fits to the glass face or surface. As such the pressing force is dispersed over the entire longitudinal-directional portion of the blade rubber. The blade rubber makes contact with the glass face with a uniformly distributed pressure.
As will be explained hereinafter with reference to the drawings, despite a number of advantages, the uniform pressure distribution in a flat blade has also some disadvantages. Compared to a traditional blade, which allows more movement and flexibility (due to its superstructure and linkages), the rubber fixes extremely well. This rigid design does not always lead to an improved wiping performance. At low speeds of driving, the blade has full contact with the window screen. As driving speed of a vehicle increases, the wind forces tend to lift the wiper blade. Due to this lifting, the vision area is no longer sufficiently covered by the wiper. Additionally, the behaviour of a flat blade at the points of reversal, i.e. the upper and lower dead centers of the blade, may be improved.